1. Field of the Invention
This invention relates to a process for the recovery of organic oils and organic residues from inorganic or mineral solids by solvent extraction, and for the recovery of solvent used for the extraction.
2. Description of the Prior Art
The removal of organic oils and residues from mineral solids, such as sand, sandstone, shale, limestone and other porous mineral materials, is a commerically desirable process. The raw material is abundant, and extracted organic oils and residues may be utilized as fuel. Prior art methods to recover oils and residues from such mineral materials have not achieved satisfactory efficiency.
One method for removing organic oils from mineral solids is to heat the oil containing solids and separate organic oils and residues by distillation. Utilization of this method, however, causes a substantial portion of the organic oils to decompose due to the high temperatures required for distillation. The internal structure of the inorganic material being treated may also be altered by the high temperatures resulting in trapping of the organic oils.
Another method of extracting organic oils and residues from mineral solids is to wash the oil containing solids with hot water, thereby extracting organic oils to the water phase. The emulsion of oil in water is difficult to separate, and the overall process is slow and inefficient.
Various solvent extraction systems are known to the art. Some solvent extraction systems are used in combination with hot water treatments, while others provide solvent extraction without addition of water. British Pat. No. 654,753, for example, teaches a solvent extraction method wherein bituminous coal is immersed in ethylene dichloride. Solvent is removed from the treated coal by draining and/or centrifuging, and by evaporation when the coal is subsequently dried and the solvent recovered from the oil by distillation.
U.S. Pat. No,. 4,238,315 teaches a process for recovering oil from oil shale containing kerogen by heating in the presence of an organic solvent to a temperature in the range of about 385.degree. to 440.degree. C. under elevated pressure of 250 to 2000 psig and thereafter recovering the extracted oil. Solvent and oil are separated from the spent shale by filtration, settling, or centrifuging and solvent is separated from the oil by factionation. U.S. Pat. No. 4,139,450 discloses a process for solvent extraction of bitumen from tar sands by a substantially "water-free" process wherein tar sand is first mixed with a hot solvent such as toluene at 180.degree. to 280.degree. C. to evaporate water from the tar sands. The bitumen and solids are separated by settling and filtration or centrifugation of fines and hot organic solvent vapors recycled to the feed mixer for heat exchange with incoming tar sands. Residual organic solvent is steam stripped from the bitumen and the solvent recycled.
U.S. Pat. No. 2,487,788 teaches a process for treating kerogen containing shale with a hydrocarbon oil at 375.degree. to 425.degree. C. to convert kerogen solids to predominantly liquid products which are miscible in the oil. Any remaining oil associated with the treated shale may be recovered by displacement with steam or gases. The oil products are subsequently fractionated to separate components as desired.
U.S. Pat. No. 2,173,842 teaches a process for solvent extraction of organic oils from mineral solids by forced displacement and forced circulation of solvent through pores followed by vaporization and then repeating the cycle.
U.S. Pat. No. 2,133,280 teaches solvent extraction of oil products from mineral solids using a non-oleaginous solvent followed by treatment of the mineral residue with a petroleum solvent.
U.S. Pat. No. 3,392,455 teaches a process for solvent extraction of oils from solids, such as from soybeans, with removal of a major portion of solvent from the solids by thermal treatment with vaporized solvent and pressure variation by movement through a desolventizer by a spiral lifting cage conveyor. Residual solvent, up to 10 percent of the solvent entrained, may be reduced by stripping with fresh, clean steam resulting in solvent contaminated steam which requires further treatment for recovery of solvent.
U.S. Pat. No. 1,123,222 teaches a solids rotatable drum drier utilizing heated air or products of combustion for drying solids.
Organic solvent extraction of oils and organic residues from inorganic or mineral solids without the addition of water is preferable to aqueous extraction of oils which requires further separation of oil from the water.